This invention relates to a semiconductor device and a method for manufacturing the same, and more particularly to a semiconductor device having a multi-layered wiring structure and a method for manufacturing the same.
Recently, various types of LSIs are used in the main portions of computers and communication devices and the performances of the computers and communication devices are closely related to the performance of the LSI itself. The performance of the LSI itself can be improved by enhancing the integration density thereof, that is, reducing the size of elements.
Since the aspect ratio of the contact hole increases as the size of the element is reduced, it is difficult to form a continuous conductive layer in a plug because of breakage of a wiring metal in the plug, that is, breakage of the wiring metal at a stepped portion when the wiring metal is formed by the conventional sputtering method. Therefore, a method for embedding tungsten in the plug and forming a wiring metal (an aluminum alloy in most cases) thereon is used. However, with this method, since a metal embedded in the plug and a wiring metal are different from each other, there occur problems that the reliability is lowered, different tools are required for embedding the metal into the plug and forming the wiring metal and the number of steps is increased.
In order to solve the above problems, the reflow technique for simultaneously forming the plug and the wiring metal is studied. The reflow technique is a technique for causing a metal to flow by use of the high-temperature sputtering method or the like, but most of the reflow techniques now studied are to form stacked several wiring layers at the same reflow temperature.
When the metal wirings of several layers are formed at the same reflow temperature by use of the reflow technique, the metal wiring of the underlying layer is subjected to the same heat treatment several times and a void occurs therein to lower the reliability of the wiring.